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System Grounding and Component Grounding.


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Hi Chaps.

Quick one. From what I can gather from the american law. All metal objects in a solar system needs to be grounded. I might be getting confused between earthing and grounding.

May I earth all the metal objects(at their reccomended groudning points) to the common ground in our AC distribution board? Thus keeping all the entire systems metal componets at equal potential differecne between them if static etc to build up.

1)Component Grounding for solar panel rails and solar frame- some reccomend a seperate earth rod and the ground cable to run outside your house incase of lightning , this will keep the flash out your home. However with a lightning surge protection in the combiner box on the roof, this will anyway accomodate for this? If you put the solar on a different earth rod there could be a potential difference between other items grounded seperarly.?

2) chassis of inverters and metal boxes, may this be on common ground - the one in the AC DB board?

3) finaly battery grounding, usually done on the negegtive pole according to system. May this also be done on the common ground point in the AC DB?

Thanks guys, how does this all work? i see USA NEC have a great handbook. Its to smart for me though.

L

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Usually any metal component housing should be grounded and it should not cause any harm to any of the components if you do so using the recommended grounding points.  All these grounding points should also be connected to the house ground / common ground in the AC DB (as you mentioned). 

 

Lightning (basically anything) will always take the path of least resistance.  You can ground your PV panels (and frames) by means of a cable directly from the panels to an earth-rod to help when lightning strikes the panels, but you should also connect that to the normal house ground in order to eliminate possible potential differences between the separate grounds.

 

I will not advise anybody to ground the batteries UNLESS your specific inverter installation documentation clearly states that you may ground e.g. the battery negative.  If the installation instructions of the inverter does not clearly indicate that you may do this, you might damage your inverter.

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You will always get galvanic corrosion between dissimilar metals, just more between certain metals and less between others.  The potential difference between zinc (plated) and aluminium is much lower than between copper and aluminium - if you would make use of the zinc plated clips or lugs the corrosion should be much less than between copper and aluminium.  If you are inland you should also have less worries than if you are close to the sea.

 

http://en.wikipedia.org/wiki/Galvanic_corrosion

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Comments on Point 2:

 

If you install a separate DC earth electrode then that earth electrode must be bonded to the AC electrode. If you don't bond them together you could end up having a large potential difference between the two earthing systems under fault condition. (e.g lightning strike) This potential difference could lead to unsafe touch potentials.

 

To properly disperse a lightning strike you need a low impedance path to earth for it. So having multiple earth electrodes bonded together is a good idea to achieve that.

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  • 2 months later...

So, would one need to run a separate copper wire to each panel, or would the metal (aluminium) frames of the panels and panel mounts be sufficient?

 

All the professional installations have separate copper wire running from panel to panel and which is eventually earthed. I think I've read somewhere that that is a requirement, but I might be mistaken.

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All the professional installations have separate copper wire running from panel to panel and which is eventually earthed. I think I've read somewhere that that is a requirement, but I might be mistaken.

Any idea on how thick this earth cable should be?

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All the professional installations have separate copper wire running from panel to panel and which is eventually earthed. I think I've read somewhere that that is a requirement, but I might be mistaken.

I guess that's because copper is a better conductor of electricity, than aluminium? makes sense

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If lightning does strike your panels, it is over. No wire will stop that kind of destructive force.

 

But, and here I am guilty, if panels are not earthed, and you work on them and there is a problem somewhere, it could be a shocking experience.

Also in weather conditions, the panels can build up a charge apparently. Earthing them comes in handy again.

 

But a lightning strike ... it is still over and done. Get new panels, controller, new inverter, sommer alles new.  :D

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I guess that's because copper is a better conductor of electricity, than aluminium? makes sense

 

Actually aluminium is an excellent conductor and at the thicknesses of the average rails for holding panels will do a much better job than some measly thin copper wire..

From what I understand it is more just because 'thats what the panel manufacturers say in the instructions' and because it is difficult to ensure that all the aluminium peices bond to one another electrically.

The seperate peices are usually anodised which needs to be peirced to conduct electricity and then further aluminum oxide also forms a non conductive skin.

There are special components for this - http://www.we-llc.com/products/weeb-washer - if this link doesn't work google 'weeb washer' to find many hits on it - to me this is a far *better* way of doing it, it makes way more sense.

Anyway this brings me to my question, does anyone know somewhere local that has this sort of product available or could make such a thing?

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Most of the time 4mm2 bare copper wire is used.

 

2.5mm2 is sufficient as long as the earth continuity does not exceed 0.2ohm.

 

Comments on Point 2:

 

If you install a separate DC earth electrode then that earth electrode must be bonded to the AC electrode. If you don't bond them together you could end up having a large potential difference between the two earthing systems under fault condition. (e.g lightning strike) This potential difference could lead to unsafe touch potentials.

 

To properly disperse a lightning strike you need a low impedance path to earth for it. So having multiple earth electrodes bonded together is a good idea to achieve that.

 

Impedance must 10ohm or less.

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